As is typical with acetylenic compounds, the acetylenic complexes of the invention change color in response to environmental stimuli due to polymerization via 1,4- addition reactions involving the acetylenic moieties, upon exposure to such environmental stimuli.
Acetylenic compounds that undergo color changes in response to some stimulii are known to the art. For example, acetylenic compounds having at least one --C.tbd.C--C.tbd.C--, have been disclosed as time-temperature history indicators in U.S. Pat. No. 3,999,946 (Patel et al.). Patel et al. discloses monomeric acetylenic compounds of the formula, R--C.tbd.C--C.tbd.C--R, where R includes an alkyl, aryl, benzoate, sulfonate, urethane, acid or alcohol moiety. The compounds disclosed by Patel et al. are colorless and are polymerizable in the solid state, either thermally or by actinic radiation. As the polymerization proceeds, these compounds undergo a contrasting color change to blue or red, and in some instances the color intensifies with time until the compounds finally develop into metallic-looking polymers. Thus, the compounds can be used as time-temperature history indicators and as radiation-dosage indicators. The reference also described polymers of the type [C.tbd.C--CH.sub.2).sub.m OCONH(CH.sub.2).sub.6 NHOCO(CH.sub.2).sub.m --C.tbd.C].sub.n where m is 2, 3 or 4 and n is large, wherein a polymer containing polymeric repeating units of the same empirical formula, undergoes color changes upon thermal annealing.
Other exemplary U.S. patents relating to acetylenic compounds and their use as environmental indicating materials include U.S. Pat. Nos. 4,215,208 (thermochromic materials), 4,125,534 (carbazolyl diacetylenes), and 4,189,399 (co-crystallized compositions).
G. Wegner in an article entitled "Topochemical Polymerization of Monomers with Conjugated Triple Bonds" in Die Makromolekulare Chemie 154, pp. 35-48 (1972) discloses acetylenic compounds having at least one --C.tbd.C--C.tbd.C-- moiety and two urea moieties, the urea moieties being separated from the diacetylene by a phenylene moiety. However, the compounds disclosed by Wegner were not very reactive and did not exhibit color changes that would be useful in monitoring environmental exposure.
None of the publications disclose or suggest complexation of acetylenic compounds to produce acetylenic complexes whose reactivity to environmental stimuli is amenable to control. Acetylenic compounds in the art usually display reactivity immediately after synthesis, thus requiring special handling during processing and shipping of articles fabricated from them. Certain of the complexes of the present invention provide a solution to this problem, as complexation provides an alteration in the reactivity of the acetylenic compounds contained in the complexes, even to the extent of complete inactivity. Reactivity is then reinstated at the desired time point by contact with an appropriate reactivating agent.
In other embodiments of the present invention, the reactivity of acetylenic compounds to stimuli is enhanced upon complexation. In further embodiments of the present invention, complexes react spontaneously with moisture, undergoing a readily perceptible color change, thus making them quite useful in moisture indicators.